1. Field of the Invention
The present invention relates to a dielectric ceramic composition, and an electronic device comprising a dielectric layer comprised of the dielectric ceramic composition, and further specifically, relates to a dielectric ceramic composition preferable to be used in mid-high voltage applications with high rated voltage (e.g. 100V or more), and electronic device.
2. Description of the Related Art
Recently, it is highly demanded to downsize an electronic device along with densification of electronic circuit. With a rapid progress in downsizing and increasing capacitance of a multilayer ceramic capacitor, applications are expanding, and the required properties are varied.
For example, a mid-high voltage capacitor used at high rated voltage (e.g. 100V or more) can be preferably used in a device such as ECM (engine electric computer module), fuel injector, computerized throttle, inverter, converter, HID headlamp unit, battery control unit of hybrid engine, and digital still camera.
Therefore, when using a mid-high voltage capacitor in the above devices, heat generation due to densified mounting of an electronic device and hard use environment as typified by those of an electronic device for automobile cause problems, so that it is expected to provide a capacitor, usable under high voltage, having small temperature change rate of capacitance, especially at a high temperature of 100° C. or more, and highly reliable.
To address such demands, for example, the Japanese Unexamined Patent Publication 2005-217000 proposes a multilayer ceramic capacitor having a dielectric layer with a constitution that concentrations of Mg, Mn and rare earth element in crystal grain are gradually increased from a core of the crystal grain to crystal grain boundary.
Also, the Japanese Unexamined Patent Publication 2001-230149 proposes a multilayer ceramic capacitor having a dielectric layer comprised of dielectric particle with core-shell structure, wherein a shell portion includes an acceptor type element (such as Mn), Mg and rare earth element, and concentrations of the acceptor type element and rare earth element included in the shell portion are gradually increased from a boundary between the core portion and the shell portion to crystal grain boundary.
Further, in the Japanese Unexamined Patent Publication 2001-230148, there is proposed a multilayer ceramic capacitor having a dielectric layer comprised of dielectric particle which is solid solution, wherein concentrations of an acceptor type element such as Mn, and rare earth element such as Ho, included in the dielectric particle, are gradually increased from a core of the particle to crystal grain boundary.
However, in the multilayer ceramic capacitor disclosed in the Japanese Unexamined Patent Publication 2005-217000, test voltage of IR (insulation resistance) lifetime is as low as 4.75V/μm, indicating this is not for use under high voltage. On the other hand, the Japanese Unexamined Patent Publication 2001-230149 only describes that the disclosed multilayer ceramic capacitor is preferred to have capacitance-temperature characteristic satisfying B characteristic, indicating this is not for use at high temperature. Also, the multilayer ceramic capacitor disclosed in the Japanese Unexamined Patent Publication 2001-230148 only satisfies F characteristic for capacitance-temperature characteristic, indicating this is not for use at high temperature as with the Japanese Unexamined Patent Publication 2001-230149.
Also, in a multilayer ceramic capacitor using a dielectric ceramic composition having barium titanate showing ferroelectricity as a main component, when applying electric field, electrostrictive phenomenon, i.e. generation of mechanical distortion, occurs. Vibration noise caused by vibration due to the electrostrictive phenomenon may be in the noise level uncomfortable for men, so that countermeasures are required.